From b0ddfb9b65344109c55e75ced8a33af4aaea7050 Mon Sep 17 00:00:00 2001
From: Norman Maurer <nmaurer@redhat.com>
Date: Sun, 1 Jun 2014 19:24:30 +0200
Subject: [PATCH] [#2525] Use VoidChannelPromise in MessageToMessageEncoder
 when possible

Motivation:
At the moment MessageToMessageEncoder uses ctx.write(msg) when have more then one message was produced. This may produce more GC pressure then necessary as when the original ChannelPromise is a VoidChannelPromise we can safely also use one when write messages.

Modifications:
Use VoidChannelPromise when the original ChannelPromise was of this type

Result:
Less object creation and GC pressure
---
 .../handler/codec/MessageToMessageEncoder.java   | 16 ++++++++++++++--
 1 file changed, 14 insertions(+), 2 deletions(-)

diff --git a/codec/src/main/java/io/netty/handler/codec/MessageToMessageEncoder.java b/codec/src/main/java/io/netty/handler/codec/MessageToMessageEncoder.java
index d0e98efa44..1a2cc034c2 100644
--- a/codec/src/main/java/io/netty/handler/codec/MessageToMessageEncoder.java
+++ b/codec/src/main/java/io/netty/handler/codec/MessageToMessageEncoder.java
@@ -108,9 +108,21 @@ public abstract class MessageToMessageEncoder<I> extends ChannelOutboundHandlerA
         } finally {
             if (out != null) {
                 final int sizeMinusOne = out.size() - 1;
-                if (sizeMinusOne >= 0) {
+                if (sizeMinusOne == 0) {
+                    ctx.write(out.get(0), promise);
+                } else if (sizeMinusOne > 0) {
+                    // Check if we can use a voidPromise for our extra writes to reduce GC-Pressure
+                    // See https://github.com/netty/netty/issues/2525
+                    ChannelPromise voidPromise = ctx.voidPromise();
+                    boolean isVoidPromise = promise == voidPromise;
                     for (int i = 0; i < sizeMinusOne; i ++) {
-                        ctx.write(out.get(i));
+                        ChannelPromise p;
+                        if (isVoidPromise) {
+                            p = voidPromise;
+                        } else {
+                            p = ctx.newPromise();
+                        }
+                        ctx.write(out.get(i), p);
                     }
                     ctx.write(out.get(sizeMinusOne), promise);
                 }